The present invention relates to color measurement engines, and more particularly to engines including parallel detectors.
Color measurement engines are well known and widely used in a variety of color measurement instruments. Typically, the engine includes a source of illumination for illuminating a sample, one or more detectors for detecting light reflected from (or transmitted through) the sample, and one or more filters for filtering the reflected (or transmitted) light. The detectors measure the light at various frequencies within the visible spectrum and provide an output indicative of the measured light.
In the detector portion, a conventional technique is to include a single detector and a plurality of filters, and a mechanism for sequentially positioning the filters in front of the detector for serial measurements. Optics are included between the sample and the detector to focus the sample target area onto the sensor. Another technique is to include a single detector, a plurality of filters, and a light switch that sequentially directs the light passing through the filters to the detector for serial measurements. Both of these techniques have the disadvantage of serial processing of the different frequencies of light, which results in two problems. First, a significant period of time is required to acquire a color measurement. Second, in situations where the sample and the engine are moving relative one another, a different portion of the sample is in the field of view as each different frequency of light is measured. Consequently, a single color measurement does not relate to a single location on the sample, but rather is a hybrid of a range of locations.
Yet another technique in the detector portion is to include a plurality of detectors, each with its own filter. This technique permits parallel processing of the data. However, the plurality of detectors involves high part counts, leading to increased material and labor expense. This technique also involves the optical challenge of directing the light flux efficiently onto each detector. Typically, an optical system (e.g. fiber optics) is provided for each detector to direct light to the detector. Typically these optical systems are complex and expensive. If a simple optical system is used, the measurement efficiency will be low because the light energy is distributed over a large circular region with only a small percentage of that region corresponding to active detector area.